In the related art, a warning device is considered which warns a driver about obstacles existing around a vehicle. For example, in a warning device disclosed in Patent Literature 1, obstacles around a vehicle and the direction of eyes of a driver are detected, respectively, and it is determined whether or not the driver recognizes the obstacles by the comparison of the positions of the detected obstacles with the direction of eyes. Furthermore, the warning device warns about the obstacles which are determined not to be recognized by the driver.